Polyolefin composition containing low viscosity propylene homopolymer, fiber and extensible non-woven fabric prepared therefrom

ABSTRACT

A polyolefin composition which contains 45 to 5 weight percent of a low viscosity propylene homopolymer having an as polymerized melt flow rate of 250 to 550 g/10 minutes and 55 to 95 weight percent of an olefin polymer composition, preferably a random copolymer of propylene and ethylene and/or a C 4-10  alpha-olefin or mixtures thereof, containing from 90 to 99 weight percent propylene. The composition may be formed into fibers having a diameter of from 15 to 23 microns. The fibers may be used to produce nonwoven fabrics.

This application is division of Ser. No. 09/589,472, filed Jun. 7, 2000and U.S. Pat. No. 6,476,135.

BACKGROUND OF THE INVENTION

The present invention relates to a polyolefin composition containing acrystalline propylene homopolymer having a high melt flow rate, and anolefin polymer composition, as well as fiber and nonwoven fabricprepared therefrom. Nonwoven fabrics prepared from fibers of thispolyolefin composition exhibit a desirable combination of acceptabletensile strength, superior cross-directional fabric elongation, goodprocessability, and improved fabric softness and drape.

U.S. Pat. No. 5,460,884 discloses a nonwoven fabric prepared from apolyolefin composition having a highly crystalline propylene homopolymeras a major component and a heterophasic ethylene/propylene randomcopolymer as a minor component. The nonwoven fabric is said to be verystrong but yet soft in comparison to comparable nonwoven fabrics.

Nonwoven fabrics have gained acceptance in various products, includingdiapers, disposable medical products and personal hygiene products.Nonwoven fabrics destined for use in these applications may be subjectedto post-manufacturing finishing operations such as coating orstretching. Fabrics having high tensile strength can be difficult toprocess, and also may exhibit inadequate suppleness (“drape”) as well asreduced fabric elongation.

Nonwoven fabrics prepared from polyolefin fibers having a high melt flowrate have been proposed. Thus, U.S. Pat. No. 5,529,850 discloses fibersand nonwoven fabrics produced from crystalline propylene polymers andcopolymers having a polydispersity index of 2.5 to 3.7 and a melt flowrate of from 600 to 2000 g/10 minutes.

An object of this invention is to provide a polyolefin compositioncapable of being formed into fibers of fine diameter.

Another object of this invention is to provide a polyolefin fibercapable of being formed into a nonwoven fabric having a combination ofdesirable properties, including acceptable tensile strength, superiorcross-directional fabric elongation, good processability, and improvedfabric softness and drape.

A feature of this invention is a polyolefin composition which includesan as-polymerized, high melt flow rate (MFR) propylene homopolymer and arandom copolymer of propylene and ethylene and/or a C₄₋₁₀ alpha-olefin.

Another feature of this invention is a fiber prepared from thispolyolefin composition and which has a diameter of from 15 to 23microns.

Yet another feature of this invention is a nonwoven fabric prepared fromthis polyolefin fiber and which has superior cross-directional fabricelongation, as measured by peak tensile elongation.

An advantage of the nonwoven fabric of the present invention is that ithas improved processability, softness and drape.

SUMMARY OF THE INVENTION

The present invention relates to a polyolefin composition comprising:

A. 45 to 5 weight percent of a low viscosity propylene homopolymerhaving an as polymerized MFR of from 250 to 550 g/10 minutes, asmeasured by D-1238, Condition L (230° C./2.16 Kg); and

B. 55 to 95 weight percent of an olefin polymer composition selectedfrom the group consisting of

(1) a random copolymer of propylene and ethylene and/or a C₄₋₁₀alpha-olefin, with the copolymer containing from 90 to 99 weight percentpropylene;

(2) a propylene polymer composition consisting essentially of:

(a) from 30 to 65% of a copolymer of propylene with a C₄₋₈ alpha-olefin,which contains from 80 to 98% propylene, and

(b) from about 35 to 70% of a copolymer of propylene with ethylenehaving an ethylene content of from 1 to 10% or a terpolymer of propylenewith ethylene and a C₄₋₈ alpha-olefin having a total comonomer contentis from 2 to 10%;

(3) an olefin polymer composition consisting essentially of:

(a) from 10 to 50% of a propylene homopolymer having an isotactic indexof from 80 to greater than 99%, or a copolymer selected from the groupconsisting of (i) propylene and ethylene, (ii) propylene, ethylene and aCH₂═CHR alpha-olefin, where R is a C₂₋₈ straight or branched alkyl, and(iii) propylene and a CH₂═CHR alpha-olefin, where R is a C₂₋₈ straightor branched alkyl, wherein said copolymer contains from 85 to 99%propylene, and having an isotactic index greater than 80 to 98%,

(b) from 5 to 20% of a semi-crystalline, essentially linear copolymerfraction having a crystallinity of about 20 to 60%, by differentialscanning calorimetry (DSC), wherein the copolymer is selected from thegroup consisting of (i) ethylene and propylene containing over 55%ethylene; (ii) ethylene, propylene, and a CH₂═CHR alpha-olefin, where Ris a C₂₋₈ straight or branched alkyl, containing from 1 to 10% of thealpha-olefin and over 55% up to 98% of both ethylene and alpha-olefin;and (iii) ethylene and a CH₂═CHR alpha-olefin, where R is a C₂₋₈straight or branched alkyl, containing over 55% up to 98% of saidalpha-olefin, which copolymer is insoluble in xylene at room or ambienttemperature, and

(c) from 40 to 80% of a copolymer fraction selected from the groupconsisting of a copolymer of (i) ethylene and propylene wherein thecopolymer contains from 20% to less than 40% ethylene; (ii) ethylene,propylene, and a CH₂═CHR alpha-olefin, where R is a C₂₋₈ straight orbranched alkyl, wherein the alpha-olefin is present in an amount of from1 to 10% and the amount of ethylene and alpha-olefin present is from 20%to less than 40%; and (iii) ethylene and a CH₂═CHR alpha-olefin, where Ris a C₂₋₈ straight or branched alkyl, containing from 20 to less than40% of the alpha-olefin, and optionally with 0.5 to 10% of a diene, saidcopolymer fraction being soluble in xylene at ambient temperature, andhaving an intrinsic viscosity of from 1.7 to 3.0 dl/g, wherein the totalamount of ethylene units or said alpha-olefin units in the olefinpolymer composition, or of ethylene and said alpha-olefin units whenboth are present in the olefin polymer composition is from 15 to 35%,the total amount of (b) and (c) fractions, based on the total olefinpolymer composition is from about 65% to 80%, the weight ratio of(b)/(c) is from 0.1 to about 0.3 and the total content of ethylene orC₄₋₈ alpha-olefin or combination thereof in (b+c) is less than 50%;

(4) a thermoplastic olefin composition consisting essentially of:

(a) from 10 to 60% of a propylene homopolymer having an isotactic indexgreater than 90 or a crystalline propylene copolymer with ethyleneand/or C₄₋₈ alpha-olefin having a propylene content greater than 85% andan isotactic index of greater than 85%;

(b) from 30 to 60% of an amorphous ethylene-propylene copolymerfraction, optionally containing minor amount of a diene, which is xylenesoluble at room temperature, and contains from 40 to 70% ethylene; and

(c) from 8 to 40% of a semi-crystalline ethylene-propylene copolymerwhich is xylene insoluble at room temperature,

(5) a linear low density polyethylene containing up to 20%, by weight,of a C₄₋₈ α-olefin having a density of from 0.88 to 0.945 g/cm³ and amelt index of from 0.1 to 35 g/10 min;

(6) a high melt strength propylene polymer having a branching index ofless than 0.9 or a melt tension of 3 to 28 cN; and

(7) mixtures thereof.

The present invention also relates to fibers prepared from thispolyolefin composition, with the fibers having a diameter of from 15 to23 microns.

In another embodiment, the present invention is a nonwoven fabricprepared from fibers made from the polyolefin composition.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The polyolefin composition of the present invention contains from 5 to45, preferably 5 to 40, and most preferably 10 to 40, weight percent ofa low viscosity propylene homopolymer. The propylene homopolymer may beprepared by polymerization of propylene using known Ziegler-Nattacatalyst systems and according to known methods operating in liquidphase comprising the propylene monomer or a solution thereof, in analiphatic or aromatic hydrocarbon solvent, or in gas phase, or combiningliquid and gas polymerization steps.

The polyolefin composition of the present invention also contains from55 to 95, preferably 60 to 95 weight percent, and most preferably from60 to 90 weight percent of an olefin polymer composition B, which may beany one of several olefin compositions B(1) through B(5) or mixturesthereof. The olefin polymer composition is preferably B(1), a randomcopolymer of propylene and ethylene and/or a C₄₋₁₀ alpha-olefin. Therandom copolymer contains from 90 to 99, preferably from 95 to 98, mostpreferably from 96.5 to 99, weight percent propylene, with the balancebeing ethylene, a C₄₋₁₀ alpha-olefin, a mixture of both ethylene and aC₄₋₁₀ alpha-olefin or a mixture of C₄₋₁₀ alpha-olefins. Examples ofrandom copolymers that can be used as olefin polymer composition B(1)include propylene/ethylene, propylene/1-butene, propylene/1-pentene,propylene/1-octene and propylene/ethylene/1-butene copolymers.

The random copolymer may be prepared from the respective monomers byconventional copolymerization using conventional apparatus andtechniques well known to those of ordinary skill in the art. Randomcopolymers of propylene and ethylene with or without 1-butene arecommercially available from companies such as Montell USA, Inc.

The random copolymer has a MFR of at least 10, preferably 10 to 40, g/10minutes, as measured according to D-1238, Condition L (230° C./2.16Kg.). These melt flow rate values may be obtained directly inpolymerization, or by visbreaking.

The olefin polymer composition may alternatively be B(2), a propylenepolymer composition consisting essentially of:

(a) from 30 to 65%, preferably from about 45 to 65%, of a copolymer ofpropylene with a C₄₋₈ alpha-olefin, which contains from 80 to 98%propylene, and preferably from 85 to 95%, and

(b) from about 35 to 70%, preferably from about 35 to 55%, of acopolymer of propylene with ethylene having an ethylene content of from1 to 10%, preferably from 7 to 9%, or a terpolymer of propylene withethylene and a C₄₋₈ alpha-olefin having a total comonomer content, i.e.,of ethylene and a C₄₋₈ alpha-olefin, is from 2 to 10%, preferably 3 to6%, and the ethylene content is preferably from 1 to 3%.

The olefin polymer composition may alternatively be B(3), which consistsessentially of:

(a) from 10 to 50% of a propylene homopolymer, preferably from 10 to40%, and most preferably from 20 to 35%, having an isotactic index offrom 80 to greater than 99%, preferably from 85 to 99%, or a copolymerselected from the group consisting of (i) propylene and ethylene, (ii)propylene, ethylene and a CH₂═CHR alpha-olefin, where R is a C₂₋₈straight or branched alkyl, and (iii) propylene and a CH₂═CHRalpha-olefin, where R is a C₂₋₈ straight or branched alkyl, wherein saidcopolymer contains from 85 to 99%, and preferably from 90 to 99%propylene and having an isotactic index greater than 80 to 98%,preferably greater than 85 to 98%,

(b) from 5 to 20% of a semi-crystalline, essentially linear copolymerfraction, preferably from 7 to 15%, having a crystallinity of about 20to 60%, by differential scanning calorimetry (DSC), wherein thecopolymer is selected from the group consisting of (i) ethylene andpropylene containing over 55% ethylene; (ii) ethylene, propylene, and aCH₂═CHR alpha-olefin, where R is a C₂₋₈ straight or branched alkyl,containing from 1 to 10% of the alpha-olefin and over 55% up to 98%,preferably from 80 to 95%, of both ethylene and alpha-olefin; and (iii)ethylene and a CH₂═CHR alpha-olefin, where R is a C₂₋₈ straight orbranched alkyl, containing over 55% up to 98%, preferably from 80 to95%, of said alpha-olefin, which copolymer is insoluble in xylene atroom or ambient temperature, and

(c) from 40 to 80% of a copolymer fraction, preferably 50 to 70%,selected from the group consisting of a copolymer of (i) ethylene andpropylene wherein the copolymer contains from 20% to less than 40%,preferably from 20 to 38%, most preferably 25 to 38% ethylene; (ii)ethylene, propylene, and a CH₂═CHR alpha-olefin, where R is a C₂₋₈straight or branched alkyl, wherein the alpha-olefin is present in anamount of from 1 to 10%, preferably from 1 to 5%, and the amount ofethylene and alpha-olefin present is from 20% to less than 40%; and(iii) ethylene and a CH₂═CHR alpha-olefin, where R is a C₂₋₈ straight orbranched alkyl, containing from 20 to less than 40%, preferably 20 to38%, and most preferably 25 to 38% of the alpha-olefin, and optionallywith 0.5 to 10%, preferably 1 to 5% of a diene, said copolymer fractionbeing soluble in xylene at ambient temperature, and having an intrinsicviscosity preferably of from 1.7 to 3.0 dl/g, wherein the total amountof ethylene units or said alpha-olefin units in the olefin polymercomposition, or of ethylene and said alpha-olefin units when both arepresent in the olefin polymer composition is from 15 to 35%, the totalamount of (b) and (c) fractions, based on the total olefin polymercomposition is preferably from about 65% to 80%, the weight ratio of(b)/(c) is preferably from 0.1 to about 0.3 and the total content ofethylene or C₄₋₈ alpha-olefin or combination thereof in (b+c) is lessthan 50%, and preferably from 20 to 45%.

The olefin polymer composition may alternatively be B(4), athermoplastic olefin composition consisting essentially of:

(a) from 10 to 60% of a propylene homopolymer, preferably from 20 to50%, having an isotactic index greater than 90, preferably greater than98%, or a crystalline propylene copolymer with ethylene and/or C₄₋₈alpha-olefin having a propylene content greater than 85% and anisotactic index of greater than 85%;

(b) from 30 to 60% of an amorphous ethylene-propylene copolymerfraction, preferably from 30 to 50%, optionally containing minor amountof a diene, which is xylene soluble at room temperature, and containsfrom 40 to 70% ethylene; and

(c) from 8 to 40% of a semi-crystalline ethylene-propylene copolymerwhich is xylene insoluble at room temperature.

The olefin polymer composition may alternatively be B(5), a linear lowdensity polyethylene containing up to 20%, preferably 5 to 14% of a C₄₋₈α-olefin. Preferably, said linear low density polyethylene has a densityof from 0.89 to 0.94, and most preferably from 0.900 to 0.935 g/cm³. Themelt index [ASTM D1238, Condition E (190° C./2.16 Kg)] is preferablyfrom 0.20 to 33 g/10 min., and most preferably from 0.20 to 30 g/10 min.

The olefin polymer composition may alternatively be B(6), a high meltstrength propylene polymer can be prepared from a propylene polymerusing the irradiation process disclosed in U.S. Pat. No. 5,554,668, thedisclosure of which is incorporated herein by reference or by theprocess disclosed in U.S. Pat. No. 5,047,485, the disclosure of which isincorporated by reference. Suitable propylene polymers include ahomopolymer of propylene, a copolymer of propylene with ethylene or aC₄₋₁₀ α-olefin, a heterophasic or impact modified propylene polymer ormixtures thereof. Such propylene polymers are commercially available.

The branching index quantifies the degree of long chain branchingpresent in the high melt strength propylene homopolymer. It is definedby the equation:$g^{\prime} = \frac{\lbrack{IV}\rbrack_{Br}}{\lbrack{IV}\rbrack_{Lin}}$

in which g′ is the branching index, [IV]_(Br) is the intrinsic viscosityof the branched propylene polymer and [IV]_(Lin) is the intrinsicviscosity of the corresponding, linear propylene polymer ofsubstantially the same molecular weight average molecular weight.

The melt tension of the second component is preferably 8 to 26 cN, morepreferably 12 to 24 cN. Melt tension provides an indication of the meltstrength of the material, and may be determined with a Gottfert Rheotensmelt tension apparatus from Gottfert Inc. by measuring the tension of astrand of molten polymer in centi-Newtons as follows: the polymer to beexamined is extruded at 180° C. through a capillary 20 mm long and 2 mmin diameter; the strand is then subjected to stretching using a drawingsystem with a constant acceleration of 0.3 cm/sec². The tensionresulting from the above drawing is measured (in centi-Newtons). Thehigher the melt tension means the greater the melt strength valueswhich, in turn, are indicative of the particular material's strainhardening ability.

The olefin polymer composition may alternatively be mixtures of B(1)through B(6).

Olefin polymer compositions B(2) through B(4) are disclosed in evengreater detail in U.S. Pat. No. 5,508,318, the disclosure of which isincorporated by reference herein.

The olefin polymer composition B(5) is disclosed in greater detail inU.S. Pat. No. 5,455,303, the disclosure of which is incorporated byreference.

The catalysts that can be used to produce the polymer composition of thepresent invention are well known in patent literature. Particularlysuited are the catalysts described in U.S. Pat. Nos. 4,339,054,5,539,067 and 5,618,771. Other examples of catalysts are described inU.S. Pat. Nos. 4,472,524 and 4,473,660.

The above mentioned catalysts used in the polymerization comprise theproduct of the reaction between:

a) a solid component, containing a titanium compound and anelectron-donor compound (internal electron donor) supported on magnesiumchloride in active form,

b) an aluminum alkyl compound (cocatalyst) and

c) an electron-donor compound (external electron-donor).

These catalysts are preferably capable of producing propylenehomopolymer having an isotactic index higher than 90%.

The solid catalyst component (a) contains as electron-donor a compoundselected among the ethers, ketones, lactones, compounds containing N, Pand/or S atoms, and mono- and dicarboxylic acid esters.

Suitable electron-donors for solid catalyst component (a) includemonobenzyl monobutyl phthalate; malonic acid esters such as diisobutyland diethyl malonate; alkyl and arylpivalates; alkyl, cycloalkyl andaryl maleates; alkyl and aryl carbonates such as diisobutyl carbonate,monoethyl monophenyl carbonate, and diphenyl carbonate; succinic acidesters such as mono- and diethyl succinate. Particularly suitable arephthalic acid esters such as diisopropyl, di-n-butyl, dilsobutyl,di-n-pentyl, diisopentyl, dihexyl, diheptyl and dioctyl phthalate. Otherelectron-donors particularly suited are the 1,3-diethers of formula (I):

wherein R, R^(I), R^(II), R^(III), R^(IV) and R^(V) are the same ordifferent and are H, C₁₋₁₈ linear or branched alkyl, C₅₋₁₈ cycloalkyl,C₆₋₁₈ aryl, C₇₋₁₈ alkylaryl or C₇₋₁₈ arylaklyl radicals, provided thatwhen R is H or alkyl, R^(I) is other than H or alkyl and when R^(I) is Hor alkyl, R is other than H or alkyl; R^(VI) and R^(VII) are the same ordifferent and are C₁₋₁₈ linear or branched alkyl, C₅₋₁₈ cycloalkyl,C₆₋₁₈ aryl, or C₇₋₁₈ arylaklyl radicals; and two or more of R R^(v) maybe bonded to form a cyclic structure having 5 to 18 carbon atoms.Illustrative examples of ethers whose structures conform to formula (I)include 2,2-diphenyl-1,3-dimethoxypropane,2,2-dibenzyl-1,3-dimethoxypropane, 2,2-bis(cyclohexylmethyl)1,3-dimethoxypropane, 1,3-bix(methoxymethyl)cyclohexane and2,2′-bix(methoxymethyl)norbornane,2-methyl-2-isopropyl-1,3-dimethoxypropane,2,2-diisobutyl-1,3-dimethoxypropane, and 2-isopropyl-2-cyclopentyl-1,3-dimethoxy propane. The diethers of the type describedare disclosed in U.S. Pat. No. 5,095,153, the disclosures of which areincorporated herein by reference

The preparation of the described catalyst components is done accordingto various methods. One of them consists of milling or co-milling themagnesium dihalide (used in the anhydrous state containing less than 1%water), together with the titanium compound, and the electron-donorcompound under conditions where the magnesium dihalide is activated; themilled product is then treated one or more times with excess TiCl₄ attemperatures from 80 to 135° C., and subsequently washed repeatedly witha hydrocarbon (hexane, for example) until the chlorine ions havedisappeared from the wash waters. The electron-donor compound may alsobe added during the milling operation or during the treatment withexcess TiCl₄. If more than one treatment with excess TiCl₄ is employed,the electron donor compound is added during the first treatment.

According to another method the anhydrous magnesium halide ispreactivated according to known methods, and then treated one or moretimes with excess TiCl₄ containing the electron-donor compound insolution. In this case the operation also takes place at a temperaturefrom 80 to 135° C. Optionally, the TiCl₄ treatment is repeated. Thesolid is then washed with hexane or other solvents to eliminate alltraces of unreacted TiCl₄. The electron-donor compound may also be addedduring the treatment with excess TiCl4, preferably during the firsttreatment, if more than one treatment with excess TiCl₄ is used.

According to another method, a MgCl₂nROH adduct (particularly in theform of spherical particles) where n is generally a number ranging from1 to 3 and ROH is ethanol, butanol or isobutanol, is treated one or moretimes with excess TiCl₄ containing the electron-donor compound insolution. The electron-donor compound may also be added during thetreatment with excess TiCl₄, preferably during the first treatment, ifmore than one treatment with excess TiCl₄ is used. The reactiontemperature generally ranges from 80 to 120 ° C. After the reaction thesolid is isolated and treated one or more times with TiCl₄, and thenwashed with a hydrocarbon solvent until all traces of unreacted TiCl₄have been eliminated.

According to yet another method, magnesium alcoholates andchloroalcoholates (the chloroalcoholates can be prepared according toU.S. Pat. No. 4,220,554) are treated one or more times with excess TiCl₄containing the electron-donor compound in solution, operating under thesame conditions already described. The electron-donor compound may alsobe added during the treatment with excess TiCl4, preferably during thefirst treatment, if more than one treatment with excess TiCl₄ is used.

The titanium compound in the solid catalyst component, expressed as Ticontent, is generally present in the amount ranging from 0.5 to 10% byweight, and the quantity of the electron-donor compound that remains seton the solid magnesium dihalide usually ranges from 5 to 20% in moleswith respect to the magnesium dihalide.

Titanium compounds which can be used for the preparation of catalystcomponents are halides or halogen alcoholates. Titanium tetrachloride isthe preferred compound. Satisfactory results are obtained also withtitanium trihalides, particularly TiCl₃HR (HR=Hydrogen Reduced),TiCl₄ARA (ARA=Aluminum Reduced and Activated), and with titanium halidealcoholates such as TiCl₃OR, where R is a phenyl radical.

The preparations indicated above lead to the formation of activatedmagnesium dihalide. Besides the ones already mentioned, other reactionsare known in the art which lead to the formation of activated magnesiumdihalides starting from magnesium compounds which are different from themagnesium halides, such as magnesium carboxylates.

The active form of magnesium halides in the solid catalyst component canbe recognized by the fact that in the X-ray spectrum of the catalystcomponent the major intensity reflection presents a width at half-peakat least greater than 30% with respect to the major intensity reflectionwhich appears in the spectrum of the nonactivated magnesium dihalide, orby the fact that the major intensity reflection (which appears in thespectrum of the nonactivated magnesium halides, having a surface areasmaller than 3 m²/g) is absent and in its place there is a halo with themaximum intensity shifted with respect to the position of the maximumintensity reflection of the nonactivated magnesium dihalide. The mostactive forms of magnesium halide are those where the X-ray spectrumshows a halo.

Among the magnesium dihalides, the magnesium chloride is the preferredcompound. In the case of the most active forms of magnesium chloride,the X-ray spectrum of the catalyst component shows a halo instead of thereflection, which in the spectrum of the nonactivated magnesium chlorideis situated at the distance of 2.56 Å.

As cocatalysts (b), one preferably uses the trialkyl aluminum compounds,such as Al-triethyl, Al-triisobutyl and Al-tri-n-butyl. Other examplesof cocatalysts (b) are the linear or cyclic Al-alkyl compoundscontaining two or more Al atoms bonded by means of O, or N atoms, or bySO₂, SO₃ or SO₄ groups. Some examples of these compounds are:

(C₂H₅)₂—Al—O—Al(C₂H₅)₂

(C₂H₅)₂—Al—N(C₆H₅)—Al(C₂H₅)₂

(C₂H₅)₂—Al—SO₂—Al—(C₂H₅)₂

CH₃—[(CH₃)Al—O—]_(n)—Al(CH₃)₂

—[(CH₃)Al—O]_(n)—

wherein n is a number from 1 to 20.

In general, the Al-Alkyl compound is present in quantities that allowthe Al/Ti ratio to vary from 1 to 1000.

The electron-donor compounds (c) that can be used as externalelectron-donors comprise the aromatic acid esters (such as alkylicbenzoates), heterocyclic compounds (such as the2,2,6,6-tetramethylpiperidine and 2,6-diisopropylpiperidine), and inparticular silicon compounds containing at least one Si—OR bond (where Ris a hydrocarbon radical). Some examples of silicon compounds are:(tert-C₄H₉)₂ Si(OCH₃)₂ and (C₆H₅)₂Si(OCH₃)₂. Suitable silicon compoundsare described in U.S. Pat. Nos. 5,539,067 and 5,618,771 and U.S. Ser.No. 08/469,735, the disclosures of which are incorporated herein byreference.

The 1,3-diethers of formula (I) are also suitable to be used as externaldonors. In the case that the internal donor is one of the 1,3-diethersof formula (I), the external donor can be omitted.

The catalysts can be precontacted with small quantities of olefins(prepolymerization), maintaining the catalyst in suspension in ahydrocarbon solvent, and polymerizing at temperatures ranging fromambient to 60° C. The quantity of polymer produced is from 0.5 to 3times the weight of the catalyst.

The prepolymerization can also be carried out in liquid propylene underthe temperature conditions indicated above, and can produce quantitiesof polymer that can reach up to 1000 g per gram of catalyst component.

The propylene homopolymer has a MFR of from 250 to 550, preferably 350to 450, and most preferably 380 to 420 g/10 minutes, as measured by ASTMD-1238, Condition L (230° C./2.16 Kg). These MFR values are obtaineddirectly in polymerization (“as polymerized”), and not bypost-polymerization (visbreaking) techniques well known to those ofordinary skill in this art.

Propylene homopolymers suitable for use in the present invention arecommercially available from Montell USA Inc.

The polyolefin composition of the present invention may be prepared bymixing together the olefin polymer composition and propylene homopolymerusing conventional techniques and apparatus well known to those ofordinary skill in the art. For example, the two components may be mixedtogether in a mixer, and extruded into pellets using a single screwconventional extruder operated at conventional temperatures and mixingspeeds.

The polyolefin composition has a MFR of 20 to 70 g/10 minutes,preferably 25 to 65 g/10 minutes, as measured according to D-1238,Condition L (230° C./2.16 Kg)

The molecular weight distribution of a polymer (MWD) is defined as theweight average molecular weight (Mw) divided by the number averagemolecular weight (Mn).

The polyolefin composition of the present invention typically has apolydispersity index of from 3.0 to 4.5, preferably from 3.3 to 3.7, andmost preferably from 3.5 to 3.7. Polydispersity Index (P.I.) is aparameter obtained by way of rheologic measurement, and which iscorrelated to the polymer's molecular weight distribution. Inparticular, the lower the P.I., the narrower the MWD.

The polyolefin composition preferably includes one or more organicphosphites and/or phosphonites, one or more HALS (Hindered Amine LightStabilizer) and one or more phenolic antioxidants. Specific examples ofphosphites include tris(2,4-di-tert-butylphenyl)phosphite marketed byCiba Specialty Chemicals Corp. under the trademark Irgafos 168;distearyl pentaerythritol diphosphite marketed by GE Specialty Chemicalsunder the trademark Weston 618;4,4′-butylidenebis(3-methyl-6-tert-butylphenyl-di-tridecyl)phosphitemarketed by Ashasi Denka under the trademark ADK Stab P;tris(monononylphenyl)phosphite; bis(2,4-di-tert-butyl) pentaerythritoldiphosphite, marketed by GE Specialty Chemicals under the trademarkUltranox 626.

HALS are monomeric or oligomeric compounds containing in the moleculeone or more substituted amine, preferably piperidine, groups. Specificexamples of HALS containing substituted piperidine groups are thecompounds sold by Ciba Specialty Chemicals Corp. under the followingtrademarks:

Chimassorb 944; Tinuvin 770, Tinuvin 765, Tinuvin 622, Tinuvin 144, andthe product sold by Cytec Industries Inc. under the trademark Cyasorb UV3346.

Illustrative examples of phenolic antioxidants includetris-(4-tert-butyl-3-hydroxy-2,6-dimethylbenzyl)-s-triazine-2,4,6-(1H,3H,5H)trione;calcium bi[monoethyl(3,5-di-tert-butyl-4-hydroxy-benzyl)phosphonate];1,3,5-tris(3,5-di-tert-butyl-4-hydroxybenzyl)-s-triazine-2,4,6(1H,3H,5H)trione;1,3,5-tri-methyl-2,4,6-tris(3,5-di-tert-butyl-4-hydroxybenzyl)benzene;pentaerythrityl-tetrakis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate]; octadecyl-3-(3,5-di-tert-butyl-4-hydroxyphenyl) propionate;and 2,6-dimethyl-3-hydroxy-4-tert-butylbenzyl abietate.

A preferred stabilizer package comprises 200-400 ppm Irgafos 168tris(2,4-di-tert-butylphenyl)phosphite; 200-400 ppm Tinuvin 622poly(N-beta-hydroxymethyl-2,2,6,6-tetramethyl-4-hydroxy-piperidylsuccinate) hindered amine light stabilizer; and 200-400 ppm calciumstearate. These stabilizers can be added to the polyolefin compositionby means of an extruder with subsequent pelletization or surfacecoating, or they can be mechanically mixed with the polyolefins.

Other additives conventionally used in the production of continuouspolymer filaments can also be incorporated in the polyolefin polymercomposition such as UV stabilizers, pigments, delusterants, lubricants,antistatic agents, water and alcohol repellents, etc. in conventionalamounts, which are typically no more than about 10% by weight.

The polyolefin composition of the present invention may be manufacturedinto fibers and films using conventional techniques and apparatus wellknown to those of ordinary skill in the art. Thus, for example, thecomposition may be extruded through a spinnerette into a fiber orfilament which is then oriented and quenched prior being wound onto abobbin. Alternatively, the extruded fiber may be immediately formed intoa non-woven fabric using known techniques such as spunbonding,meltblowing, needlepunching, air-layering etc. The term “nonwovenfabric” means a web having a structure of individual fibers or threadswhich are interlaid, but not in a regular, repetitive manner as in aknitted fabric. The fibers of the present invention have particularutility as starting materials for the production of nonwoven fabrics.

Fibers prepared from the composition of the present invention typicallyhave a fiber diameter of from 15 to 23 microns, preferably 16 to 17.5microns, and most preferably 16 to 17 microns.

The spunbond process generally uses a hopper which supplies polymer to aheated extruder, which supplies molten polymer to a spinnerette wherethe polymer is formed into a plurality of filaments by passing itthrough the holes of the spinnerette. The filaments are usually quenchedwith air at a low pressure, drawn, usually pneumatically, and depositedon a moving foraminous mat, belt or “forming wire” to form the nonwovenfabric. Spunbonding processing temperatures generally range from about175° C. to 320° C.

“Cross-directional peak elongation” is the fabric elongation when fabricstrength is at its peak. “Cross directional elongation” is the maximumelongation at which the fabric fails. CD elongation is higher than CDpeak elongation.

At a given fiber diameter, fabric elongation will generally be highestwhen the fabric is bonded at the optimum bonding temperature. Fabricelongation decreases with a decrease in fabric weight.

The nonwoven fabrics of the present invention have superiorcross-directional fabric elongation, as measured by peak tensileelongation, and relatively low tensile strength. Thus, the nonwovenfabrics of the present invention preferably have a peak tensileelongation of at least 80%, still more preferably at least 100%, andmost preferably a peak tensile elongation of at least 120%, as measuredby ASTM D-5035, at a fabric weight of from 21 to 26 g/m². Such non-wovenfabrics will exhibit a desirable combination of processability (e.g.,high melt spinning speeds of at least 4000 meters/minute at a melttemperature of 220° C.) and improved “drape” when manufactured intononwoven articles or nonwoven components of articles such as diapers,disposable medical products, e.g., hospital gowns, and personal hygieneproducts, e.g., sanitary napkins.

In a preferred embodiment, the nonwoven fabric of the present inventionhas a relatively low tensile strength of less than 750 g/cm, as measuredby ASTM D-5035. It is preferred that the nonwoven fabric's tensilestrength be less than 700 g/cm, even more preferred if the tensilestrength is less than 600 g/cm, and most preferred if the tensilestrength is about 350 g/cm.

EXAMPLES

The following Examples are intended to illustrate specific embodimentsof the present invention, and are not to be construed to limit thepermissible scope of the invention in any manner whatsoever.

Example I

Polyolefin compositions were converted into spunbond fabric sampleshaving a fabric weight of 25 grams/M² using a Reifenhauser II spunbondmachine. The homopolymers were extruded at 450° F., while the polyolefincompositions were extruded at 415° F. Fabric prepared from thehomopolymers was bonded at 270° F., while fabric prepared from thepolyolefin compositions was bonded at 250° F. Fabric testing wasperformed according to ATSM D-5035, Strip Tensile, using 1×6 inchsamples and a crosshead speed of 12 inches/minute. Five specimens weretested per sample to arrive at average fabric elongation and tensilestrength.

TABLE 1 Sam- Vis- ple Comp. MFR broken P.I. Fiber CD Tens. CD Elong I-1100% PP 35 Yes 2.3 17.3 750 77% I-2 100% PP 35 No 3.6 17.9 688 98% I-3 80% I-1 65 Blend 3.7 17.5 623 80% I-4 100% 35 Yes 2.1 17.8 596 54% I-5100% 38 No 3.4 22.4 615 80% I-6 100% 53 No 3.3 21.5 604 77% I-7  80% I-53 No 3.6 16.9 583 157%  * Homopolymer of propylene having an aspolymerized MFR of 400, commercially available from Montell USA Inc.

Several observations can be taken from Table I:

1. Sample I-4 (a visbroken random propylene/ethylene copolymer having aMFR of 35 g/10 min) produced a nonwoven fabric having a lower peakelongation than nonwoven fabric produced from sample I-1 (a visbrokenpropylene homopolymer having a MFR of 35 g/10 min).

2. Sample I-5 (a random copolymer having an as polymerized MFR of 38g/10 min.) produces poorly formed nonwoven fabric having coarse hand anda peak elongation comparable to visbroken propylene homopolymer having aMFR of 35 g/10 min (sample I-1).

3. Sample I-2 (a propylene homopolymer having an as polymerized MFR of35 g/10 min.) produced a nonwoven fabric having a peak elongationsuperior to that of sample I-1 (propylene homopolymer visbroken to a MFRof 35 g/10 min.)

4. Sample I-7 (a polyolefin composition of the present invention)produced a non-woven fabric having a clearly superior peak elongation.

Example II

Polyolefin compositions were prepared and formed into non-woven fabricsusing the general procedures of Example 1 but using different equipment.The fabric produced had a fabric weight of 22 g/m². Sample descriptionsare set forth in Table 2, sample characteristics are set forth in Table3, and sample elongation and tensile strengths are reported in Table 4.

TABLE 2 Sample Description Sample No. Description MFR II-1 propylenehomopolymer 35 II-2 random copolymer¹ 38 II-3 random copolymer² 52 II-480% II-2 + 20% propylene homopolymer³ 60 II-5 80% II-2 + 10% propylenehomopolymer² 44 II-6 63% random copolymer⁴ 39 37% propylene homopolymer²

TABLE 3 Sample Characteristics Sample No. Max Spin Speed m/min. P.I.II-1 4950 2.24 II-2 4580 3.39 II-3 5780 3.31 II-4 4340 3.53 II-5 44203.46 II-6 3420 3.89

TABLE 4 Comparison of Maximum Elongation and Corresponding Tensile CD MDSample No. Elongation Elongation CD Tensile MD Tensile (1) For FiberSize 16.5 Microns II-1 60 60 1.7 3 II-2 85 90 1.3 2.2 II-3 85 90 1.7 2.3II-4 120 90 2.3 2.5 II-5 100 90 1.7 2.5 II-6 105 90 1.9 2.7 (2) ForFiber Size 19 microns II-1 60 60 1.4 2.5 II-2 100 75 1.4 1.8 II-3 110 901.4 1.8 II-4 90 90 1.8 1.8 II-5 85 85 1.4 2 II-6 110 90 1.6 2.3

The following observations can be drawn from this data:

1. Sample II-4 [a polyolefin composition comprising 20% by weightpropylene homopolymer having an as polymerized MFR of 400 g/10 min. and80% by weight of a random propylene/ethylene copolymer (3% ethylene)having an as polymerized MFR of 38 g/10 min.] produced a nonwoven fabrichaving the highest fabric elongation among the samples tested.

2. Sample II-6 [a polyolefin composition comprising 37% by weightpropylene homopolymer having an as polymerized MFR of 400 g/10 min. and63% by weight of a random propylene/ethylene copolymer (3% ethylene)having an as polymerized MFR of 10 g/10 min.] produced a nonwoven fabrichaving peak elongation comparable to Sample II-4. However, sample II-6was more difficult to spin at a 16.5 micron fiber diameter than sampleII-4.

What is claimed is:
 1. A fiber prepared from a composition comprising:A. 45 to 5 weight percent of a low viscosity propylene homopolymerhaving an a polymerized melt flow rate of from 250 to 550 g/10 minutes,and B. 55 to 95 weight percent of an olefin polymer composition selectedfrom the group consisting of (1) a random copolymer of propylene andethylene and/or a C₄₋₁₀ alpha-olefin, with the copolymer containing from90 to 99 weight percent propylene; (2) a propylene polymer compositionconsisting essentially of: (a) from 30 to 65% of a copolymer ofpropylene with a C₄₋₈ alpha-olefin, which contains from 80 to 98%propylene, and (b) from about 35 to 70% of a copolymer of propylene withethylene having an ethylene content of from 1 to 10% or a terpolymer ofpropylene with ethylene and a C₄₋₈ alpha-olefin having a total comonomercontent of from 2 to 10%; (3) an olefin polymer composition consistingessentially of: (a) from 10 to 50% of a propylene homopolymer having anisotactic index of from 80 to greater than 99%, or a copolymer selectedfrom the group consisting of (i) propylene and ethylene, (ii) propylene,ethylene and a CH₂═CHR alpha-olefin, where R is a C₂₋₈ straight orbranched alkyl, and (iii) propylene and a CH₂═CHR alpha-olefin, where Ris a C₂₋₈ straight or branched alkyl, wherein said copolymer containsfrom 85 to 99% propylene, and having an isotactic index greater than 80to 98%, (b) from 5 to 20% of a semi-crystalline, essentially linearcopolymer fraction having a crystallinity of about 20 to 60%, bydifferential scanning calorimetry (DSC), wherein the copolymer isselected from the group consisting of (i) ethylene and propylenecontaining over 55% ethylene; (ii) ethylene, propylene, and a CH₂═CHRalpha-olefin, where R is a C₂₋₈ straight or branched alkyl, containingfrom 1 to 10% of the alpha-olefin and over 55% up to 98% of bothethylene and alpha-olefin; and (iii) ethylene and a CH₂═CHRalpha-olefin, where R is a C₂₋₈ straight or branched alkyl, containingover 55% up to 98% of said alpha-olefin, which copolymer is insoluble inxylene at room or ambient temperature, and (c) from 40 to 80% of acopolymer fraction selected from the group consisting of a copolymer of(i) ethylene and propylene wherein the copolymer contains from 20% toless than 40% ethylene; (ii) ethylene, propylene, and a CH₂═CHRalpha-olefin, where R is a C₂₋₈ straight or branched alkyl, wherein thealpha-olefin is present in an amount of from 1 to 10% and the amount ofethylene and alpha-olefin present is from 20% to less than 40%; and(iii) ethylene and a CH₂═CHR alpha-olefin, where R is a C₂₋₈ straight orbranched alkyl, containing from 20 to less than 40% of the alpha-olefin,and optionally with 0.5 to 10% of a diene, said copolymer fraction beingsoluble in xylene at ambient temperature and having an intrinsicviscosity of from 1.7 to 3.0 dl/g, wherein the total amount of ethyleneunits or said alpha-olefin units in the olefin polymer composition, orof ethylene and said alpha-olefin units when both are present in theolefin polymer composition is from 15 to 35%, the total amount of (b)and (c) fractions, based on the total olefin polymer composition is fromabout 65% to 80%, the weight ratio of (b)/(c) is from 0.1 to about 0.3and the total content of ethylene or C₄₋₈ alpha-olefin or combinationthereof in (b+c) is less than 50%; (4) a thermoplastic olefin consistingessentially of: (a) from 10 to 60% of a propylene homopolymer having anisotactic index greater than 90 or a crystalline propylene copolymerwith ethylene and/or C₄₋₈ alpha-olefin having a propylene contentgreater than 85% and an isotactic index of greater than 85%; (b) from 30to 60% of an amorphous ethylene-propylene copolymer fraction, optionallycontaining a minor amount of a diene, which is xylene soluble at roomtemperature, and contains from 40 to 70% ethylene; (c) from 8 to 40% ofa semi-crystalline ethylene-propylene copolymer which is xyleneinsoluble at room temperature; and (5) a linear low density polyethylenecontaining up to 20%, by weight, of a C₄₋₈ α-olefin having a density offrom 0.88 to 0.945 g/cm³ and a melt index of from 0.1 to 35 g/10 min;(6) a high melt strength propylene polymer having a branching index ofless than 0.9 or a melt tension of 3 to 28 cN; and (7) mixtures thereof,said fiber having a fiber diameter of from 15 to 23 microns.
 2. Thefiber of claim 1, wherein said fiber diameter ranges from 16 to 20microns.
 3. A nonwoven fabric comprising the fiber of claim 1, andhaving a peak tensile elongation of at least 80%, at a fabric weight offrom 21 to 26 g/m².
 4. The nonwoven fabric of claim 3, wherein said peaktensile elongation is at least 100%.
 5. The nonwoven fabric of claim 4,wherein said peak tensile elongation is at least 120%.
 6. The nonwovenfabric of claim 3, wherein a tensile strength of said fabric is lessthan 750 g/cm.
 7. The nonwoven fabric of claim 3, wherein said tensilestrength is less than 700 g/cm.